Thin film transistor array panel with varying coupling capacitance between first and second pixel electrodes

ABSTRACT

A thin film transistor array panel comprising an insulating substrate; a plurality of first signal lines formed on the insulating substrate; a plurality of second signal lines intersecting the first signal lines in an insulated manner to define pixel areas; a plurality of first pixel electrodes formed in each of the pixel areas; a plurality of thin film transistors having three electrodes respectively connected to the first signal line, the second signal line, and the first pixel electrode; and a plurality of second pixel electrodes formed in each of the pixel areas and electrically coupled with the first pixel electrodes, wherein the pixels include red, green, and blue pixels, and coupling capacitances between the first pixel electrodes and the second pixel electrodes are different among the red, green, and blue pixels. An LCD using such a thin film transistor array panel shows improved side visibility and has a wide viewing angle.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a liquid crystal display and a thinfilm transistor array panel.

2. Description of the Related Art

A liquid crystal display (LCD) is one of the most widely used flat paneldisplays. An LCD includes two panels provided with field-generatingelectrodes, and a liquid crystal (LC) layer interposed therebetween. TheLCD displays images by applying voltages to the field-generatingelectrodes to generate an electric field in the LC layer, whichdetermines orientations of LC molecules in the LC layer to adjustpolarization of incident light.

The LCD has a disadvantage of a narrow viewing angle. Various techniquesfor enlarging the viewing angle have been suggested, and a techniqueutilizing a vertically aligned LC and providing cutouts or protrusionsat field-generating electrodes such as pixel electrodes and a commonelectrode is promising.

To describe the method of providing cutouts in more detail, pixelelectrodes and a common electrode respectively have cutouts, the cutoutsinduce a slanted electric field, and the slanted electric field controlsfalling directions of liquid crystals. Control of the falling directionof liquid crystals makes it possible to widen the viewing angle ofliquid crystal display. To describe the method of providing protrusionsin more detail, protrusions are formed on both of pixel electrodes and acommon electrode, the protrusions induce a slanted electric field, andthe slanted electric field controls falling directions of liquidcrystals.

Other methods in which pixel electrodes have cutouts and protrusionsformed on a common electrode is also possible to control fallingdirections of liquid crystals. An LCD using cutouts or protrusions hasan excellent viewing angle of over 80 degrees in any direction, in viewof the contrast ratio where 1:10 is a standard contrast ratio and inview of gray scale inversion where a viewing angle of occurringbrightness inversion is a standard angle. However, such an LCD showspoor visibility that is even inferior to a twisted nematic mode LCD. Thepoor visibility is caused by discordance of the gamma curve between thefront view and side view. For example, in a vertically aligned mode LCDusing cutouts, as the viewing angle is increased, the picture planebecomes brighter and the color shifts toward white. When this phenomenonis excessive, the image is distorted because the brightness differencebetween gray scales disappears. As the use of the LCD is widened toinclude multimedia displays, the visibility becomes more important.

SUMMARY OF THE INVENTION

An object of the present invention is to provide an LCD having improvedvisibility. To achieve such an object, a pixel area includes two pixelelectrodes, different voltages are applied to the two pixel electrodes,and a voltage difference between the two pixel electrodes is differentamong red, green, and blue pixels.

Concretely, a thin film transistor array panel comprises: an insulatingsubstrate; a plurality of first signal lines formed on the insulatingsubstrate; a plurality of second signal lines intersecting the firstsignal lines in an insulated manner to define pixel areas; a pluralityof first pixel electrodes formed in each of the pixel areas; a pluralityof thin film transistors having three electrodes respectively connectedto the first signal line, the second signal line, and the first pixelelectrode; and a plurality of second pixel electrodes formed in each ofthe pixel areas and electrically coupled with the first pixelelectrodes, wherein the pixels include red, green, and blue pixels andcoupling capacitances between the first pixel electrode and the secondpixel electrode are different among the red, green, and blue pixels.

The thin film transistor array panel may further comprise a plurality ofcoupling electrodes connected to the first pixel electrode andoverlapped with the second pixel electrodes in an insulated manner. Atleast one of the first and second pixel electrodes may have a domaindividing member. The coupling electrodes may be connected to andelongated from drain electrodes of the thin film transistors. The lengthof the coupling electrodes may decrease in an order of green, red, andblue pixels, and the width of the coupling electrodes may decrease in anorder of green, red, and blue pixels. When the coupling capacitancebetween the first pixel electrode and the second pixel electrode in agreen pixel is 1, the coupling capacitance of the first pixel electrodeand the second pixel electrode in a red pixel preferably ranges from0.95 to 1.0 and that of a blue pixel preferably ranges from 0.75 to0.95.

A thin film transistor array panel comprises: an insulating substrate; aplurality of first signal lines formed on the insulating substrate; aplurality of second signal lines intersecting the first signal lines inan insulated manner to define pixel areas; a plurality of first pixelelectrodes formed in each of the pixel areas; a plurality of thin filmtransistors having three electrodes respectively connected to the firstsignal line, the second signal line, and the first pixel electrode; anda plurality of second pixel electrodes formed in each of the pixel areasand electrically coupled with the first pixel electrodes, wherein thepixels include red, green, and blue pixels and area ratios of the secondpixel electrode with respect to the first pixel electrode are differentamong the red, green, and blue pixels.

The thin film transistor array panel may further comprise a plurality ofcoupling electrodes connected to the first pixel electrode andoverlapped with the second pixel electrodes in an insulated manner. Thecoupling electrodes may be connected to and elongated from drainelectrodes of the thin film transistors. At least one of the first andsecond pixel electrodes may have a domain dividing member. The arearatios of the second pixel electrode with respect to the first pixelelectrode may increase in an order of green, red, and blue pixels. Thearea ratios of the second pixel electrode with respect to the firstpixel electrode in green, red, and blue pixels may be respectively 6:4,5.5:4.4, and 5:5.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and other advantages of the present invention will become moreapparent by describing preferred embodiments thereof in detail withreference to the accompanying drawings, in which:

FIG. 1 is a layout view of a thin film transistor array panel for an LCDaccording to an embodiment of the present invention;

FIG. 2 is a layout view of a color filter panel for an LCD according toan embodiment of the present invention;

FIG. 3 is a layout view of an LCD according to the embodiment shown inFIGS. 1 and 2;

FIG. 4 is a sectional view of the LCD shown in FIG. 3 taken along theline IV–IV′;

FIG. 5 is a circuit diagram of the LCD shown in FIGS. 1 to 4;

FIG. 6 is a layout view of a thin film transistor array panel for an LCDaccording to another embodiment of the present invention;

FIG. 7 is a sectional view of the LCD shown in FIG. 6 taken along theline VII–VII′;

FIG. 8 is a layout view of a thin film transistor array panel for an LCDaccording to another embodiment of the present invention;

FIG. 9 is a layout view of a thin film transistor array panel for an LCDaccording to another embodiment of the present invention;

FIG. 10A is a gamma curve front view.

FIG. 10B is a gamma curve upper side view.

FIG. 10C is a gamma curve diagonal side view.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The present invention now will be described more fully hereinafter withreference to the accompanying drawings, in which preferred embodimentsof the invention are shown. The present invention may, however, beembodied in many different forms and should not be construed as beinglimited to the embodiments set forth herein.

In the drawings, the thickness of layers, films, and regions areexaggerated for clarity. Like numerals refer to like elementsthroughout. It is to be understood that when an element such as a layer,film, region, or substrate is referred to as being “on” another element,it can be directly on the other element or intervening elements may alsobe present. In contrast, when an element is referred to as being“directly on” another element, there are no intervening elementspresent.

Now, liquid crystal displays and thin film transistor (TFT) array panelsfor LCDs according to embodiments of the present invention will bedescribed with reference to the accompanying drawings.

FIG. 1 is a layout view of a thin film transistor array panel for an LCDaccording to an embodiment of the present invention; FIG. 2 is a layoutview of a color filter panel for an LCD according to an embodiment ofthe present invention; FIG. 3 is a layout view of an LCD according tothe embodiment shown in FIGS. 1 and 2; and FIG. 4 is a sectional view ofthe LCD shown in FIG. 3 taken along the line IV–IV′.

An LCD according to an embodiment of the present invention includes aTFT array panel 100, a common electrode panel 200, and a LC layer 3interposed between the panels 100 and 200 and containing a plurality ofLC molecules aligned vertically to surfaces of the panels 100 and 200.

A structure of the TFT array panel 100 will now be described. Aplurality of first and second pixel electrodes 190 a and 190 b made ofindium tin oxide (ITO) or indium zinc oxide (IZO) are formed on aninsulating substrate 110 made of a transparent material such as glass.The first pixel electrode 190 a is connected to a thin film transistorand receives image data voltages. The second pixel electrode 190 b isoverlapped with a coupling electrode 176 which is connected to the firstpixel electrode 190 a. Therefore, the second pixel electrode 190 b iselectrically coupled with the first pixel electrode 190 a. Theoverlapping areas between the second pixel electrode 190 b and thecoupling electrode 176 are different among red, green, and blue pixels.

The thin film transistor connected to a gate line 121 transferringscanning signals and a data line 171 transferring image data signals.The thin film transistor switches the image data signals to be appliedor to not be applied to the first pixel electrode 190 a according to thescanning signals. The second pixel electrode 190 b has cutouts 192. Apolarizer 12 is attached to the lower surface of the insulatingsubstrate 110. When a reflective LCD is considered, the first and secondpixel electrodes 190 a and 190 b may be made of a non-transparentmaterial. In this case, the polarizer 12 is omitted.

A structure of the color filter panel will now be described. A lightblocking layer 220 to prevent light leakage, red, green, and blue colorfilters 230, and a common electrode 270 made of a transparent conductorsuch as ITO or IZO are formed on an insulating substrate 210 made of atransparent material such as glass. The common electrode 270 has cutouts271, 272, and 273. The light blocking layer 220 may be formed on areasoverlapping with the cutouts 271, 272, and 273, as well as around pixelareas to prevent light leakage due to the cutouts 271, 272, and 273.

The TFT array panel 100 will now be described in more detail withreference to FIGS. 1, 4, and 5. A plurality of gate lines 121 and aplurality of storage electrode lines 131 are formed on an insulatingsubstrate 110. The gate lines 121 extend substantially in a transversedirection and are separated from each other and transmit gate signals.Each gate line 121 has a plurality of gate electrodes 123 and expansions125 for connecting to an external circuit.

Each storage electrode line 131 extends substantially in the transversedirection and includes a plurality of sets of storage electrodes 133 a,133 b, and 133 c. Two storage electrodes 133 a and 133 b are extended ina longitudinal direction and are connected with a transverse storageelectrode 133 c. The storage line 131 may include two or more transverselines.

The gate lines 121 and the storage electrode lines 131 may have amulti-layered structure including two films having different physicalcharacteristics, i.e., a lower film (not shown) and an upper film (notshown). The upper film is preferably made of a low resistivity metalincluding an Al-containing metal such as Al or an Al alloy for reducingsignal delay or voltage drop in the gate lines 121 and the storageelectrode lines 131. On the other hand, the lower film is preferablymade of a material such as Cr, Mo, or a Mo alloy, which has good contactcharacteristics with other materials such as indium tin oxide (ITO) andindium zinc oxide (IZO). A good exemplary combination of the lower filmmaterial and the upper film material is Cr and an Al—Nd alloy. Inaddition, the lateral sides of the gate lines 121 and the storageelectrode lines 131 are tapered, and the inclination angle of thelateral sides with respect to a surface of the substrate 110 rangesabout 30–80 degrees.

A gate insulating layer 140 preferably made of silicon nitride (SiNx) isformed on the gate lines 121 and the storage electrode lines 131. Aplurality of semiconductor stripes 151 that are preferably made ofhydrogenated amorphous silicon (abbreviated to “a-Si”) are formed on thegate insulating layer 140. Each semiconductor stripe 151 extendssubstantially in the longitudinal direction, and has a plurality ofprojections 154 branched out toward the gate electrodes 123.

A plurality of ohmic contact stripes 161 preferably made of silicide orn+ hydrogenated a-Si heavily doped with n type impurity are formed onthe semiconductor stripes 151 and projections 154. The ohmic contactstripes 161 have substantially the same pattern as the semiconductorstripes 151 except for around the projections 154. Each ohmic contactstripe 161 has a plurality of projections 163, and the projections 163and the ohmic contact islands 165 are located in pairs on theprojections 154 of the semiconductor stripes 151.

A plurality of data lines 171, a plurality of drain electrodes 175, aplurality of coupling electrode 176, and a plurality of under-bridgemetal pieces 172 are formed on the ohmic contacts 161, 163, and 165 andthe gate insulating layer 140.

Each data line 171 extends substantially in the longitudinal directionand has a plurality of source electrodes 173 extending toward the drainelectrodes 175. Each data line 171 includes an expansion 179 having awider width for contact with another layer or an external device. Theunder-bridge metal piece 172 is disposed on the gate line 121.

The coupling electrode 176 is connected to the drain electrode 175 andis bent several times to have a “V” shape. The lengths of the couplingelectrodes 176 are different from each other among red, green, and bluepixels. The length of the coupling electrode 176 in the green pixel isthe longest, the length of the coupling electrode 176 in the red pixelis the second longest, and the length of the coupling electrode 176 inthe blue pixel is the shortest.

The data lines 171, the drain electrodes 175, the coupling electrodes176, and the under-bridge metal piece 172 may have a multi-layeredstructure including two films having different physical characteristics,i.e., a lower film (not shown) and an upper film (not shown). The upperfilm is preferably made of a low resistivity metal including anAl-containing metal such as Al or an Al alloy for reducing signal delayor voltage drop in the data lines. On the other hand, the lower film ispreferably made of a material such as Cr, Mo, or an Mo alloy, which hasgood contact characteristics with other materials such as indium tinoxide (ITO) and indium zinc oxide (IZO). A good exemplary combination ofthe lower film material and the upper film material is Cr and an Al—Ndalloy.

A passivation layer 180 made of an inorganic material such as siliconnitride or an organic material such as resin is formed on the data lines171, the drain electrodes 175, and the under-bridge metal piece 172. Thepassivation layer 180 has a plurality of contact holes 181 and 183respectively exposing a portion of the drain electrode 175 and theexpansion 179 of the data line 171. The passivation layer 180 and thegate insulating layer 140 have a plurality of contact holes 182, 184,and 185 respectively exposing the expansion 125 of the gate line 121 andtwo portions of the storage electrode line 131.

A plurality of pixel electrodes 190 a and 190 b, a plurality of contactassistants 95 and 97, and a plurality of storage bridges 91 are formedon the passivation layer 180. The pixel electrodes 190 a and 190 b, thecontact assistants 95 and 97, and the storage bridges 91 may be made ofa transparent conductor such as ITO and IZO, or a light reflectivematerial such as Al.

The first pixel electrode 190 a is connected to the drain electrode 175through the contact hole 181. The second pixel electrode 190 b iselectrically floated but is capacitively coupled with the first pixelelectrode 190 a, since the second pixel electrode 190 b is overlappedwith the coupling electrode 176. Therefore, the voltage of the secondpixel electrode 190 b varies dependant on the voltage of the first pixelelectrode 190 a.

The coupling capacitances formed between the first pixel electrode 190 aand the second pixel electrode 190 b are different among green, red, andblue pixels. The coupling capacitances formed between the first pixelelectrode 190 a and the second pixel electrode 190 b become smaller stepby step in an order of green, red, and blue pixels due to the lengthshortening of the coupling electrodes 176.

Differentiation of the coupling capacitances of the first pixelelectrode 190 a and the second pixel electrode 190 b among green, red,and blue pixel may be achieved by other methods, such as width anddisposition differentiation of the coupling electrode 176, rather thanby length differentiation.

When the coupling capacitance of the first sup-pixel electrode 190 a andthe second pixel electrode 190 b in the green pixel is 1, the couplingcapacitances of the first sup-pixel electrode 190 a and the second pixelelectrode 190 b in the red pixel preferably range from 0.95 to 1.0 andthat of the blue pixel preferably ranges from 0.75 to 0.95.

Cutouts 191, 193, and 194 dividing the first pixel electrode 190 a andthe second pixel electrode 190 b are classified into oblique portions191 and 193 making an angle of about 45 degrees with the gate line 121,and a longitudinal portion 194 making an angle of about 90 degrees withthe gate line 121. The two oblique portions 191 and 193 make an angle ofabout 90 degrees.

The second pixel electrode 190 b has a cutout 192 which initiates fromthe right side of the second pixel electrode 190 b and extends towardthe left side. The entrance of the cutout 191 is widened due to thecorner cut of the second pixel electrode 190 b. The first pixelelectrode 190 a and the second pixel electrode 190 b respectively make amirror image with respect to a longitudinal center line of a pixel.

The storage bridge 91 crosses over the gate line 121 and connects twostorage lines that are disposed on both sides of the gate line 121. Thestorage bridge 91 contacts the storage electrode 133 a and the storageelectrode line 131 through the contact holes 183 and 184. The storagebridge 91 overlaps the under-bridge metal piece 172. The storage bridges91 electrically connect all the storage electrode lines 131 on theinsulating substrate 110.

The storage electrode lines 131 may be used to repair defects of thegate lines 121 and the data lines 171. Such repairs are done byillumination of a laser. The under-bridge metal piece 172 helpselectrical connection of the gate line 121 and the storage bridge 91.

The contact assistants 95 and 97 are respectively connected to theexpansion 125 of the gate line 121 and the expansion 179 of the dataline 171 through the contact holes 182 and 183.

The color filter panel 200 will be described with respect to FIGS. 2, 4,and 5. A black matrix 220 for preventing light leakage is formed on aninsulating substrate 210 such as transparent glass. A plurality of red,green, and blue color filters 230 are formed on the black matrix and thesubstrate 210 and extend substantially along the columns of the pixelareas. An overcoat 250 is formed on the color filters 230 and the blackmatrix 220. A common electrode 270, preferably made of a transparentconductive material such as ITO or IZO, is formed on the overcoat 250.The common electrode 270 has a plurality of cutouts 271, 272, and 273.

A set of cutouts 271, 272, and 273 include oblique portions and endportions. The oblique portions of the cutouts 271, 272, and 273 areparallel with the oblique portions 191 and 193 of the cutout between thepixel electrodes 190 a and 190 b. The oblique portions 191 and 193 aredisposed between the oblique portions of the cutouts 271, 272, and 273.The end portions overlap the boundary line of the pixel area and includelongitudinal end portions and transverse end portions.

The LCD includes a TFT array panel 100, a color filter array panel 200facing the TFT array panel 100 and separated therefrom by apredetermined gap, and a liquid crystal layer 3 filled in thepredetermined gap. When the two panels 100 and 200 are assembled, thecutouts 271, 272, and 273 of the common electrode 270 partition the twopixel electrodes 190 a and 190 b into a plurality of sub-areas. In thepresent embodiment, as shown in FIG. 3, the two pixels 190 a and 190 bare respectively partitioned into four sub-areas. As shown in FIG. 3,each sub-area has two parallel long edges and several short edges.Therefore, the sub-areas have length direction and width direction.

Each liquid crystal 3 portion disposed between each of the sub-areas ofthe pixel electrodes 190 a and 190 b and corresponding sub-areas of thecommon electrode 270 is a sub-region. The sub-regions are classifiedinto four species according to the average long axis direction of liquidcrystals disposed therein. The sub-regions will be called a domain fromnow on.

The first pixel electrode 190 a is physically and electrically connectedto the drain electrodes 175 through the contact holes 181. The secondpixel electrode 190 b is physically and electrically floated, but isoverlapped with the coupling electrode 176 to form coupling capacitanceswith the first pixel electrodes 190 a. Therefore, the voltage of thesecond pixel electrode 190 b depends on the voltage of the first pixelelectrode 190 a. The voltage of the second pixel electrode 190 b withrespect to the common voltage is always smaller than that of the firstpixel electrode 190 a. In the meantime, when a pixel area includes twosub-areas with somewhat different electric fields, lateral visibility isimproved by the mutual compensation in the two sub-areas.

The coupling relationship between the first pixel electrode 190 a andthe second pixel electrode 190 b will be described later in detail withreference to FIG. 5. FIG. 5 is a circuit diagram of the LCD shown inFIGS. 1 to 4. In FIG. 5, Clca stands for liquid crystal (LC) capacitanceformed between the first pixel electrode 190 a and the common electrode270, and Cst stands for storage capacitance formed between the firstpixel electrode 190 a and the storage line 131. Clcb stands for liquidcrystal (LC) capacitance formed between the second pixel electrode 190 band the common electrode 270, and Ccp stands for coupling capacitanceformed between the first pixel electrode 190 a and the second pixelelectrode 190 b.

The voltage Vb of the second pixel electrode 190 b with reference to thecommon voltage and the voltage Va of the first pixel electrode 190 awith reference to the common voltage are related by the voltagedistribution law as follows:Vb=Va×[Ccp/(Ccp+Clcb)].

Since Ccp/(Ccp+Clcb) is always smaller than 1, Vb is always smaller thanVa. The capacitance Ccp can be adjusted by overlapping an area ordistance between the second pixel electrode 190 b and the couplingelectrode 176. The overlapping area between the second pixel electrode190 b and the coupling electrode 176 can be easily adjusted by changingthe width of the coupling electrode 176. The distance between the secondpixel electrode 190 b and the coupling electrode 176 can be easilyadjusted by changing the location of the coupling electrode 176. Thatis, in the present embodiment, the coupling electrode 176 is formed onthe same layer as the data line 171, but the coupling electrode 176 maybe formed on the same layer as the gate line 121. By this change, thedistance between the second pixel electrode 190 b and the couplingelectrode 176 is increased. In the meantime, voltage differences betweenthe two pixel electrodes 190 a and 190 b are different among red, green,and blue pixels due to the difference of coupling capacitance. Throughthis, a bluish tinge is diminished to improve side visibility of an LCD.

Now, the bluish tinge phenomenon will be described with reference toFIGS. 10A to 10C and the reason why the present invention diminishes thebluish tinge will be described. FIG. 10A shows gamma curves of a frontview, FIG. 10B shows gamma curves of an upper side view, and FIG. 10Cshows gamma curves of a diagonal side view.

As shown in FIGS. 10A to 10C, when an LCD is viewed from directly infront, gamma curves of red, green, and blue almost correspond. However,when an LCD is viewed from the upper side or diagonal side, gamma curvesof green and blue deviate from that of red as the gray level goes down.In particular, the gamma curve of blue severely deviates. This meansthat when an LCD is viewed from upper or diagonal sides, a ratio of bluelight increases as the gray level goes down. This is the cause of thebluish tinge.

In the present invention, a pixel area includes two pixel electrodes,different voltages are applied to the two pixel electrodes, and avoltage difference between the two pixel electrodes is different amongred, green, and blue pixels.

A coupling capacitance between the two pixel electrodes 190 a and 190 bof the blue pixel is smaller than that of the red and green pixels toalleviate an increase of the blue light ratio in the low gray level.When the coupling capacitance between the two pixel electrodes 190 a and190 b is smaller, the voltage of the second pixel electrode 190 binduced by electrical coupling with the first pixel electrode 190 a islower. Therefore, voltages applied to the second pixel electrode 190 bin the same gray level are arranged in an order of blue<red<greenaccording to their magnitude. Such voltage differences by colorsincreases as the gray level goes down. Accordingly, the ratio of bluepixel voltage with respect to green pixel voltage becomes smaller as thegray level goes down. The ratio of blue pixel voltage with respect togreen pixel voltage also becomes smaller as the gray level goes down. Asa result, the bluish tinge is alleviated.

The present invention may be applied to a twisted nematic (TN) mode TFT.Such an embodiment will be described. FIG. 6 is a layout view of a thinfilm transistor array panel for an LCD according to another embodimentof the present invention. FIG. 7 is a sectional view of the LCD shown inFIG. 6 taken along the line VII–VII′.

A plurality of gate lines 121 and a plurality of storage electrode lines131 are formed on an insulating substrate 110. The gate lines 121 extendsubstantially in a transverse direction, and are separated from eachother and transmit gate signals. The gate line 121 has a plurality ofgate electrodes 123 and expansions 125 for connecting to externalcircuit.

Each storage electrode line 131 extends substantially in the transversedirection, and includes a plurality of sets of storage electrodes 133 a,133 b, and 133 c. Two storage electrode 133 a and 133 b are extended inthe longitudinal direction and are connected with a transverse storageelectrode 133 c. The storage line 131 may include two or more transverselines.

The gate lines 121 and the storage electrode lines 131 may have amulti-layered structure including two films having different physicalcharacteristics, i.e., a lower film (not shown) and an upper film (notshown). The upper film is preferably made of a low resistivity metalincluding an Al-containing metal such as Al or an Al alloy for reducingsignal delay or voltage drop in the gate lines 121 and the storageelectrode lines 131. On the other hand, the lower film is preferablymade of a material such as Cr, Mo, or an Mo alloy, which has goodcontact characteristics with other materials such as indium tin oxide(ITO) and indium zinc oxide (IZO). A good exemplary combination of thelower film material and the upper film material is Cr and an Al—Ndalloy.

In addition, the lateral sides of the gate lines 121 and the storageelectrode lines 131 are tapered, and the inclination angle of thelateral sides with respect to a surface of the substrate 110 rangesabout 30–80 degrees.

A gate insulating layer 140 preferably made of silicon nitride (SiNx) isformed on the gate lines 121 and the storage electrode lines 131. Aplurality of semiconductor stripes 151 preferably made of hydrogenatedamorphous silicon (abbreviated to “a-Si”) is formed on the gateinsulating layer 140. Each semiconductor stripe 151 extendssubstantially in the longitudinal direction, and has a plurality ofprojections 154 branched out toward the gate electrodes 123.

A plurality of ohmic contact stripes 161 that are preferably made ofsilicide or n+ hydrogenated a-Si heavily doped with n-type impuritiesare formed on the semiconductor stripes 151 and projections 154. Theohmic contact stripes 161 have substantially the same pattern with thesemiconductor stripes 151, except for around the projections 154. Eachohmic contact stripe 161 has a plurality of projections 163, and theprojections 163 and the ohmic contact islands 165 are located in pairson the projections 154 of the semiconductor stripes 151.

A plurality of data lines 171, a plurality of drain electrodes 175, aplurality of coupling electrodes 176, and a plurality of under-bridgemetal pieces 172 are formed on the ohmic contacts 161, 163, and 165 andthe gate insulating layer 140. Each data line 171 extends substantiallyin the longitudinal direction, and has a plurality of source electrodes173 extending toward the drain electrodes 175. Each data line 171includes an expansion 179 having a wider width for contact with anotherlayer or an external device.

The under-bridge metal piece 172 is disposed on the gate line 121. Thecoupling electrode 176 is connected to the drain electrode 175. Thewidths of the coupling electrodes 176 are different from each otheramong red, green, and blue pixels. The width of the coupling electrode176 in the green pixel is the widest, the width of the couplingelectrode 176 in the red pixel is the second widest, and the width ofthe coupling electrode 176 in the blue pixel is the narrowest.

The data lines 171, the drain electrodes 175, the coupling electrodes176, and the under-bridge metal pieces 172 may have a multi-layeredstructure including two films having different physical characteristics,i.e., a lower film (not shown) and an upper film (not shown). The upperfilm is preferably made of a low resistivity metal including anAl-containing metal such as Al or an Al alloy for reducing signal delayor voltage drop in the data lines. On the other hand, the lower film ispreferably made of a material such as Cr, Mo, or an Mo alloy, which hasgood contact characteristics with other materials such as indium tinoxide (ITO) and indium zinc oxide (IZO). A good exemplary combination ofthe lower film material and the upper film material is Cr and an Al—Ndalloy.

A passivation layer 180 made of an inorganic material such as siliconnitride or an organic material such as resin is formed on the data lines171, the drain electrodes 175, and the under-bridge metal pieces 172.

The passivation layer 180 has a plurality of contact holes 181 and 183respectively exposing a portion of the drain electrode 175 and theexpansion 179 of the data line 171. The passivation layer 180 and thegate insulating layer 140 have a plurality of contact holes 182, 184,and 185 respectively exposing the expansion 125 of the gate line 121 andtwo portions of the storage electrode line 131.

A plurality of pixel electrodes 190 a and 190 b, a plurality of contactassistants 95 and 97, and a plurality of storage bridges 91 are formedon the passivation layer 180. The pixel electrodes 190 a and 190 b, thecontact assistants 95 and 97, and the storage bridges 91 may be made ofa transparent conductor such as ITO or IZO, or a light reflectivematerial such as Al.

The first pixel electrode 190 a is connected to the drain electrode 175through the contact hole 181. The second pixel electrode 190 b iselectrically floated but is capacitively coupled with the first pixelelectrode 190 a, since the second pixel electrode 190 b is overlappedwith the coupling electrode 176. Therefore, the voltage of the secondpixel electrode 190 b varies depending on the voltage of the first pixelelectrode 190 a.

The coupling capacitances formed between the first pixel electrode 190 aand the second pixel electrode 190 b are different among green, red, andblue pixels. The coupling capacitances formed between the first pixelelectrode 190 a and the second pixel electrode 190 b become smaller stepby step in an order of green, red, and blue pixels due to the widthnarrowing of the coupling electrodes 176.

As described with respect to the embodiment of FIGS. 1 to 4,differentiation of the coupling capacitances of the first sup-pixelelectrode 190 a and the second pixel electrode 190 b among green, red,and blue pixels may be achieved by other methods. In the presentinvention, width differentiation of the coupling electrode 176 isapplied.

When the coupling capacitance of the first sup-pixel electrode 190 a andthe second pixel electrode 190 b in the green pixel is 1, the couplingcapacitance of the first sup-pixel electrode 190 a and the second pixelelectrode 190 b in the red pixel preferably ranges from 0.95 to 1.0, andthat of the blue pixel preferably ranges from 0.75 to 0.95.

The first pixel electrode 190 a and the second pixel electrode 190 b arerespectively disposed in the lower half and the upper half of a pixelarea. The storage electrode 133 c is disposed between the two pixelelectrodes 190 a and 190 b.

The storage bridge 91 crosses over the gate line 121 and connects twostorage lines that are disposed on both sides of the gate line 121. Thestorage bridge 91 contacts the storage electrode 133 a and the storageelectrode line 131 through the contact holes 183 and 184. The storagebridge 91 overlaps the under-bridge metal piece 172. The storage bridges91 electrically connect all the storage electrode lines 131 on theinsulating substrate 110.

The storage electrode lines 131 may be used to repair defects of thegate lines 121 and the data lines 171. Such repairs are done byillumination of a laser. The under-bridge metal piece 172 helpselectrical connection of the gate line 121 and the storage bridge 91.

The contact assistants 95 and 97 are respectively connected to theexpansion 125 of the gate line 121 and the expansion 179 of the dataline 171 through the contact holes 182 and 183. When a pixel areaincludes two sub-areas with somewhat different electric fields, lateralvisibility is improved by the mutual compensation in the two sub-areas.

In the meantime, voltage differences between the two pixel electrodes190 a and 190 b are different among red, green, and blue pixels due tothe differences of coupling capacitance. By this, the bluish tinge isdiminished to improve side visibility of an LCD.

Another embodiment for differentiation of the coupling capacitances ofthe first pixel electrode 190 a and the second pixel electrode 190 bamong green, red, and blue pixel will now be described. FIG. 8 is alayout view of a thin film transistor array panel for an LCD accordingto another embodiment of the present invention. In the embodiment ofFIG. 8, the area ratio of the second pixel electrode 190 b to the firstpixel electrode 190 a is different among red, green, and blue pixels,but the length of the coupling electrode 176 is the same among red,green, and blue pixels. The other aspects are very similar with theembodiment of FIGS. 1 to 4.

The area ratio of the second pixel electrode 190 b to the first pixelelectrode 190 a of the green pixel is the smallest. The area ratios ofthe second pixel electrode 190 b to the first pixel electrode 190 aincrease in an order of the red pixel and the blue pixel. That is, anarea taken up by the second pixel electrode 190 b in a pixel areaincreases in an order of green, red, and blue pixels. The area ratios ofthe second pixel electrode 190 b with respect to the first pixelelectrode 190 a in the green, red, and blue pixels are preferably 6:4,5.5:4.5, and 5:5. The area ratios of the second pixel electrode 190 b tothe first pixel electrode 190 a may have various values as long as thearea ratios become larger in an order of green, red, and blue pixels.

According to the embodiments, though the same gray voltage is applied tored, green, and blue pixels, voltages of the second pixel electrodes 190b are different among red, green, and blue pixels to improve visibilityof an LCD.

FIG. 9 is a layout view of a thin film transistor array panel for an LCDaccording to another embodiment of the present invention. In theembodiment of FIG. 9, the area ratio of the second pixel electrode 190 bto the first pixel electrode 190 a is different among red, green, andblue pixels, but the width of the coupling electrode 176 is the sameamong the red, green, and blue pixels. The other aspects are verysimilar with the embodiment of FIGS. 6 and 7.

The area ratio of the second pixel electrode 190 b to the first pixelelectrode 190 a of the green pixel is the smallest. The area ratios ofthe second pixel electrode 190 b to the first pixel electrode 190 aincrease in an order of the red pixel and the blue pixel. That is, anarea taken up by the second pixel electrode 190 b in a pixel areaincreases in an order of green, red, and blue pixels. The area ratios ofthe second pixel electrode 190 b with respect to the first pixelelectrode 190 a in the green, red, and blue pixels are preferably 6:4,5.5:4.5, and 5:5. The area ratios of the second pixel electrode 190 b tothe first pixel electrode 190 a may have various values as long as thearea ratios become larger in an order of green, red, and blue pixels.

Although preferred embodiments of the present invention have beendescribed in detail hereinabove, it should be clearly understood thatmany variations and/or modifications of the basic inventive conceptsherein taught which may appear to those skilled in the present art willstill fall within the spirit and scope of the present invention, asdefined in the appended claims. In particular, cutouts in the pixel andcommon electrodes may be rearranged in various ways.

1. A thin film transistor array panel comprising: an insulatingsubstrate; a plurality of first signal lines formed on the insulatingsubstrate; a plurality of second signal lines intersecting the firstsignal lines in an insulated manner to define pixel areas; a pluralityof first pixel electrodes formed in each of the pixel areas; a pluralityof thin film transistors having three electrodes respectively connectedto the first signal line, the second signal line, and the first pixelelectrode; and a plurality of second pixel electrodes formed in each ofthe pixel areas and being electrically coupled with the first pixelelectrodes, wherein the pixels include red, green, and blue pixels, andcoupling capacitances between the first pixel electrode and the secondpixel electrode are different among the red, green, and blue pixels. 2.The thin film transistor array panel of claim 1, further comprising aplurality of coupling electrodes connected to the first pixel electrodeand overlapped with the second pixel electrodes in an insulated manner.3. The thin film transistor array panel of claim 2, wherein at least oneof the first and second pixel electrodes has a domain dividing member.4. The thin film transistor array panel of claim 2, wherein the couplingelectrodes are connected to and elongated from drain electrodes of thethin film transistors.
 5. The thin film transistor array panel of claim2, wherein the lengths of the coupling electrodes decrease in an orderof green, red, and blue pixels.
 6. The thin film transistor array panelof claim 2, wherein the widths of the coupling electrodes decrease in anorder of green, red, and blue pixels.
 7. The thin film transistor arraypanel of claim 1, wherein when the coupling capacitance between thefirst pixel electrode and the second pixel electrode in the green pixelis 1, the coupling capacitance of the first pixel electrode and thesecond pixel electrode in the red pixel ranges from 0.95 to 1.0, andthat of the blue pixel ranges from 0.75 to 0.95.
 8. A thin filmtransistor array panel comprising: an insulating substrate; a pluralityof first signal lines formed on the insulating substrate; a plurality ofsecond signal lines intersecting the first signal lines in an insulatedmanner to define pixel areas; a plurality of first pixel electrodesformed in each of the pixel areas; a plurality of thin film transistorshaving three electrodes respectively connected to the first signal line,the second signal line, and the first pixel electrode; a plurality ofsecond pixel electrodes formed in each of the pixel areas and beingelectrically coupled with the first pixel electrodes, wherein the pixelsinclude red, green, and blue pixels, and area ratios of the second pixelelectrode with respect to the first pixel electrode are different amongthe red, green, and blue pixels.
 9. The thin film transistor array panelof claim 8, further comprising a plurality of coupling electrodesconnected to the first pixel electrodes and overlapped with the secondpixel electrodes in an insulated manner.
 10. The thin film transistorarray panel of claim 9, wherein the coupling electrodes are connected toand elongated from drain electrodes of the thin film transistors. 11.The thin film transistor array panel of claim 8, wherein at least one ofthe first and second pixel electrodes has a domain dividing member. 12.The thin film transistor array panel of claim 8, wherein the area ratiosof the second pixel electrodes with respect to the first pixelelectrodes increase in an order of green, red, and blue pixels.
 13. Thethin film transistor array panel of claim 8, wherein the area ratios ofthe second pixel electrodes with respect to the first pixel electrodesin green, red, and blue pixels are respectively 6:4, 5.5:4.4, and 5:5.